1. Field of the Invention
This invention relates to the measurement of the components of a blast furnace effluent gas. More especially, this invention relates to a process for determining the nitrogen content of a blast furnace gas directly whereby supervision and regulation of the blast furnace operation is facilitated, as by means of a process computer for automatic regulation. This invention is particularly concerned with a process and apparatus for the direct determination of the nitrogen content of said gas rather than by determining the quantity of other components in said gas and calculating the nitrogen content by difference.
2. Discussion of the Prior Art
Various mathematical models have been developed in recent years which permit automation of the regulation of the blast furnace operation to such an extent that the operation can be guided with the aid of a computer.
The blast furnace gas analysis in the process models used achieves the function of a command, as the reduction behavior of the furnace can be derived therefrom. The optimal chemical capacity utilization of the reduction gas aims at decreasing the consumption of coke. Besides this ratio, material balances can be plotted from the blast furnace gas analysis and heat balances can be derived therefrom which provide information concerning melting capacity and the quality of the pig iron. The nitrogen balance, which to the prior art is substantially determined from the amount of blast air, which has been corrected as to its state, and the proportion of nitrogen in the blast furnace gas stands at first place here.
The carbon dioxide and carbon monoxide contents are determined in the previously used continuous analysis of the blast furnace gas with the aid of the infrared absorption measurement, the hydrogen content by means of the thermal conductivity measurement and the nitrogen content from the difference of the measured other gases to 100% volume. However, that results in the nitrogen content calculated from the difference being subject to the errors which may arise in determining the components CO, CO.sub.2 and H.sub.2. For example, an incorrect measurement of the CO content of 0.25% by volume and a corresponding incorrect calculation of the nitrogen content leads to the thermal economy in the lower furnace being wrongly regulated, which results in the silicon content in the pig iron of 0.23 % being changed.
Various methods are known from analytical chemistry for the analysis of nitrogen, particularly of nitrogen in bonded form, in connection with individual steel samples.
Thus, an apparatus for determining the total nitrogen of a solid sample is described in "Archiv fur das Eisenhuttenwesen", 42nd year (1971), page 878. With this apparatus the sample to be analyzed is melted in a furnace and the drawn-off extraction gas containing carbon monoxide and hydrogen as well as nitrogen is analyzed as to its total content of nitrogen. For this purpose the carbon monoxide and hydrogen are removed from the extraction gas by oxidation and the nitrogen content is then determined in an analyzer for thermal conductivity. This arrangement is not suited for the continuous measurement of the nitrogen content in the blast furnace gas.
It is an object of the invention, therefore, to improve the blast furnace regulation by improving the blast furnace gas analysis, in such a way that all constituents are constantly and continuously determined to a degree of accuracy of .+-. 0.1% by volume. The degree of accuracy should preferably be higher.